The present invention relates to an exhaust gas turbocharger, having rotor runners disposed in roller bearings, a bearing support in which the roller bearings are supported and which is supplied with lubricating oil from an oil supply of the roller bearings via a main lubricating oil duct, and a space that is concentrically arranged with respect to the roller bearings, the space representing an oil film damping gap which is pressure-fed from the lubricating oil supply of the roller bearings.
An oil film damper reduces the vibrations and shocks affecting the rotor runners of an exhaust gas turbocharger. However, the oil film damper is effective only when it is continuously fed with pressure oil. The reason is that, when the oil supply is interrupted, the oil filling of the oil film damping gap is evacuated because of the pumping effect resulting from the vibrations, and the oil film damper therefore becomes ineffective.
The roller bearings of exhaust gas turbochargers are particularly sensitive to vibrations when the rotor runners do not rotate, and the lubricating oil supply therefore is not in effect during this time. Such an operating condition occurs, for example, for an exhaust gas turbocharger of an internal-combustion engine which is part of a multi-engine system and is inoperative while vibrations and shocks are transmitted by the other operative internal-combustion engines. The same applies, in the disconnected condition, to an exhaust gas turbocharger, which can be connected and disconnected, and whose lubricating oil supply is also switched off, while the assigned internal-combustion engine is operative. Because the oil film damper is inoperable, contact corrosion will then occur between the roller bodies and the moving path of the roller bearing. Therefore, when the operation of the exhaust gas turbocharger is started, damage may occur at the roller bearing that may endanger the operation.
On the other hand, there is the risk that oil may enter into the air-carrying or gas-carrying spaces during a lubricating oil supply to the exhaust gas turbocharger which continues to operate while the rotor runners are inoperative, unless the efficiency of the seals is ensured also during the stoppage of the rotor runners by additional measures and devices. If oil were to enter, lubricating oil puddles would form in the gas-carrying spaces which, when the exhaust gas turbocharger, which was switched off, restarts, react uncontrollably with the gas flows. The leakage oil which is situated in the exhaust gas system would result in an oil fire because of an ignition at the hot exhaust gas. The leakage oil penetrated into the charge air system would be pulled along by the charge air current and would result in an overheating in the cylinders. Both would constitute extreme risks to operation.
An object of the present invention is to ensure, for an exhaust gas turbocharger which is disposed in a roller bearing and is exposed to shocks and vibrations in the inoperative position, the pressure oil supply to the oil film damping gap when the rotor runners do not rotate or rotate slowly and to avoid an entering of oil into gas-carrying spaces.
This and other objects are achieved by the present invention which provides an exhaust gas turbocharger, having rotor runners disposed in roller bearings, a bearing support in which the roller bearings are supported and which is supplied with lubricating oil from an oil supply of the roller bearings via a main lubricating oil duct, and a space that is concentrically arranged with respect to the roller bearings, the space representing an oil film damping gap which is pressure-fed from the lubricating oil supply of the roller bearings. An oil duct branches off the main lubricating oil duct for the pressure feeding of the oil film damping gap and a controllable shut-off device is coupled in the main lubricating oil duct between the oil supply and the roller bearings and which controls the pressure oil lubrication of the roller bearings.
Some of the principal advantages of the present invention are that, when the rotor runners of the exhaust gas turbocharger are stopped, the operability of the oil film damping is maintained when the pressure oil lubrication of the roller bearings is inoperative. A modification of the sealing device between the oil-carrying and gas-carrying spaces is not required for their efficiency when the rotor rollers are stopped. The exclusive oil supply of the oil film damping gap, when the rotor runners of the exhaust gas turbocharger are stopped, uses up only a small amount of oil. When the pressure oil lubrication is inoperative, oil, which emerges via the lubricating oil bores into the outer rings of the bearings from the oil film damper, results in a drip lubrication for the roller bearings. The danger of oil overflowing into the charge-air-carrying and exhaust-gas-carrying spaces of the exhaust gas turbocharger will no longer exist because of the small amount of oil emerging from the oil film damping gap.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.